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CONTENTS
Volume 24, Number 6, March25 2021
 


Abstract
The present paper has been carried out to understand the effects of impact loading on the rock tunnels, constructed in different region corresponding to varying unconfined compressive strength (UCS), through finite element method. The UCS of rockmass has substantial role in the stability of rock tunnels under impact loading condition due to falling rocks or other objects. In the present study, Dolomite, Shale, Sandstone, Granite, Basalt, and Quartzite rocks have been taken into consideration for understanding of the effect of UCS that vary from 2.85 MPa to 207.03 MPa. The Mohr-Coulomb constitutive model has been considered in the present study for the nonlinear elastoplastic analysis for all the rocks surrounding the tunnel opening. The geometry and boundary conditions of the model remains constant throughout the analysis and missile has 100 kg of weight. The general hard contact has been assigned to incorporate the interaction between different parts of the model. The present study focuses on studying the deformations in the rock tunnel caused by impacting load due to missile for tunnels having different concrete grade, and steel grade. The broader range of rock strength depicts the strong relationship between the UCS of rock and the extent of damage produced under different impact loading conditions. The energy released during an impact loading simulation shows the variation of safety and serviceability of the rock tunnel.

Key Words
rock; unconfined compressive strength; finite element analysis; tunnel; impact loading

Address
Mohammad Zaid: Department of Civil Engineering, Aligarh Muslim University, Aligarh, U.P. 202002, India

Abstract
In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause dynamic disasters, posing a major challenge for the safety of coal mine production. To improve the understanding of the dynamic disaster mechanism of gas outburst and rock burst coupling, triaxial devices are applied to axial pressure cyclic loading-unloading tests under different axial stress peaks and different pore pressures. The existing empirical formula is use to perform a non-linear regression fitting on the relationship between stress and permeability, and the damage rate of permeability is introduced to analyze the change in permeability. The results show that the permeability curve obtained had "memory", and the peak stress was lower than the conventional loading path. The permeability curve and the volume strain curve show a clear symmetrical relationship, being the former in the form of a negative power function. Owing to the influence of irreversible deformation, the permeability difference and the damage of permeability mainly occur in the initial stage of loading-unloading, and both decrease as the number of cycles of loading-unloading increase. At the end of the first cycle and the second cycle, the permeability decreased in the range of 5.777 - 8.421 % and 4.311-8.713 %, respectively. The permeability decreases with an increase in the axial stress peak, and the damage rate shows the opposite trend. Under the same conditions, the permeability of methane is always lower than that of helium, and it shows a V-shape change trend with increasing methane pressures, and the permeability of the specimen was 3 MPa > 1 MPa > 2 MPa.

Key Words
cyclic loading- unloading; axial stress; gas pressure; deformation; permeability damage rate

Address
Kai Wang,Hao Xu, Huzi Dong and Feng Du: 1.) School of Emergency Management and Safety Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
2.) Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining & Technology (Beijing), Beijing 100083, China

Yangyang Guo: 1.) School of Emergency Management and Safety Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
2.) Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources,
China University of Mining & Technology (Beijing), Beijing 100083, China
3.) Key Laboratory of Mine Disaster Prevention and Control, Shandong University of Science & Technology, Qingdao, 266590, China

Qiming Huang:Key Laboratory of Mine Disaster Prevention and Control, Shandong University of Science & Technology, Qingdao, 266590, China

Abstract
Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.

Key Words
freezing, thawing; retaining wall; temperature; groundwater level; lateral stress; overturning moment

Address
Garam Kim, Incheol Kim, Tae Sup Yun and Junhwan Lee: School of Civil and Environmental Engineering, Yonsei University, 50, Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Abstract
Since the functionally graded materials (FGMs) are used extensively as thermal barriers in many of applications. Therefore, the current article focuses on studying and presenting dynamic responses of multilayer functionally graded (FG) deep beams placed in a thermal environment that is not addressed elsewhere. The material properties of each layer are proposed to be temperature-dependent and vary continuously through the height direction based on the Power-Law function. The deep layered beam is exposed to harmonic sinusoidal load and temperature rising. In the modelling of the multilayered FG deep beam, the two-dimensional (2D) plane stress continuum model is used. Equations of motion of deep composite beam with the associated boundary conditions are presented. In the frame of finite element method (FEM), the 2D twelve –node plane element is exploited to discretize the space domain through the length-thickness plane of the beam. In the solution of the dynamic problem, Newmark average acceleration method is used to solve the time domain incrementally. The developed procedure is verified and compared, and an excellent agreement is observed. In numerical examples, effects of graduation parameter, geometrical dimension and stacking sequence of layers on the time response of deep multilayer FG beams are investigated with temperature effects.

Key Words
transient response; forced vibration; thermal effect; deep beam; multilayered functionally graded; finite element method

Address
Abdullateef H. Bashiri: Department of Mechanical Engineering, Faculty of Engineering, Jazan University, P. O. Box 45142, Jazan, Kingdom of Saudi Arabia

Seref D. Akbas: Department of Civil Engineering, Bursa Technical University, 16330, Bursa, Turkey

Alaa A. Abdelrahman: Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Amr Assie: 1.) Department of Mechanical Engineering, Faculty of Engineering, Jazan University, P. O. Box 45142, Jazan, Kingdom of Saudi Arabia
2.) Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Mohamed A. Eltaher: 1.) Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
2.) Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Elshahat F. Mohamed: Department of Mechanical Power, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Abstract
This research presents the monitoring results and their interpretation on load sharing of the pile foundation during the construction of a high-rise (124 m in height) building in Bangkok, in soft clayey ground. Axial forces in several piles, pore water pressure and earth pressures beneath the raft in a tributary area were monitored through the construction period of the building. The raft of the pile foundation in soft clayey ground can share the load up to 10-20% even though the foundation was designed using the conventional approach in which the raft resistance is ignored. The benefit from the return of ground water table as the uplift pressure is recognized. A series of parametric study by 3D-FEA were carried out. The potential of utilizing the piled raft system for the high-rise building with underground basement in soft clayey ground was preliminarily confirmed.

Key Words
3D FE; load sharing; monitoring; piled raft; soft soil

Address
Kongpop Watcharasawe and Pornkasem Jongpradist: Construction Innovations and Future Infrastructures Research Center, Department of Civil Engineering, Faculty of Engineering,
King Mongkut's University of Technology Thonburi, Thungkhru, Bangkok, Thailand

Pastsakorn Kitiyodom: Geotechnical & Foundation Engineering Co., Ltd. (GFE), Bangkok, Thailand

Tatsunori Matsumoto: Faculty of Geosciences and Civil Engineering, Kanazawa University, Kakuma-machi, Kanazawa, Japan

Abstract
The interaction of cracks and water significantly affects the fracture mechanism of rocks. In this study, laboratory tests were conducted using sandstone samples containing a single fissure to explore the hydro-mechanical behaviors in the failure process of pre-cracked rocks. The internal crack characteristics were also analyzed using X-ray CT scanning. The results show that the confining pressure has the greatest effect on the mechanical properties (e.g., strengths, elastic modulus, and Poisson's ratio), followed by the fissure inclination and water pressure. At a lower fissure inclination, the confining pressure may control the type main cracks that form, and an increase in the water pressure increases the number of anti-wing cracks and the length of wing cracks and branch cracks. However, the fracture behaviors of samples with a higher fissure inclination are only slightly affected by the confining pressures and water pressures. The effect of fissure inclination on the internal crack area is reduced with the propagation from the fissure tips to the sample ends. The fissure inclination mainly affects the value of permeability but not affect the trend. The impact of pre-existing fissure on permeability is smaller than that of confining pressure and water pressure.

Key Words
sandstone; single fissure; experiment; mechanical properties; failure behavior; permeability

Address
Tingchun Li, Yiteng Du, Qingwen Zhu, Hao Zhang and Jinlin Ran: Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation, Shandong University of Science and Technology, Qingdao 266590, China

Yande Ren: Radiology Department, The Affiliated Hospital of Qingdao University, Qingdao 266590, China


Abstract
The present study evaluates geocell reinforced slope behavior. A three dimensional analysis is carried out to simulate soil and geocell elastoplastic behavior using the finite difference software FLAC3D. In order to investigate the geocell reinforcement effect, the geocell aperture size, thickness, geocell placement condition and soil compaction had been considered as variable parameters. Moreover, a comparison is evaluated between geocell reinforcing system and conventional planar reinforcement. The obtained results showed that the pocket size, thickness and soil compaction have considerable influence on the geocell reinforcement slope performance. Moreover, it was found that the critical sliding surface was bounded by the first geocell reinforcement and the slope stability increases, by increasing the vertical space between geocell layers. In addition, the comparison between geocell and geogrid reinforcement indicates the efficiency of using cellular honeycomb geosynthetic reinforcement.

Key Words
geocell; slope stability; three dimensional; aperture size; safety factor

Address
Alireza Ardakani and Ali Namaei: Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran

Abstract
Conduits are commonly installed below the ground for utility conveyance around the world. Vertical load on a buried conduit is an important parameter that needs to be known to ensure its safe design and installation. Consideration of soil arching in load calculations helps achieve a more realistic and efficient design. In the past, considering the arching effect, the design charts have been presented for use by practicing engineers to calculate the vertical load on the conduit buried below the level ground. There are currently no design charts for calculating the vertical load on the conduit buried under a sloping ground. In this paper, an attempt has been made to present the derivation of a generalized analytical expression considering that the soil mass overlying the conduit has a sloping face and the arching phenomenon takes place. The developed generalized expression has been used to present some design charts considering specific values of slope geometry, soil properties and burial depths. Furthermore, analytical results for specific soil parameters have been compared with the results extracted from a commercial software PLAXIS 2D, for a developed numerical model and an independent study.

Key Words
arching; finite element analysis; sloping ground; soil-conduit interaction; vertical load

Address
Muhammad U. A. Khan: 1.) Geotechnical and Geoenvironmental Engineering Research Group, School of Engineering, Edith Cowan University, WA 6027, Australia
2.) Department of Civil Engineering, Mirpur University of Science and Technology, Mirpur, Azad Kashmir, Pakistan

Sanjay K. Shukla: 1.) Geotechnical and Geoenvironmental Engineering Research Group, School of Engineering, Edith Cowan University, WA 6027, Australia
2.) Department of Civil Engineering, Delhi Technological University, Delhi, India



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